The claimed invention relates generally to the field of disc drive data storage devices and more particularly, but not by way of limitation, to a method and apparatus for initializing a spindle motor after a disc drive control processor reset condition.
A disc drive is a data storage device used to store digital data. A typical disc drive includes a number of rotatable magnetic recording discs which are axially aligned and mounted to a spindle motor for rotation at a constant, high velocity. A corresponding array of read/write heads access tracks defined on the respective disc surfaces to write data to and to read data from the discs.
Control electronics are provided to direct the transfer of data between the discs and a host device. Such electronics are typically housed on an external printed circuit board (PCB) and include a control processor that provides top level control of the disc drive.
When a disc drive is initialized (i.e., comes out of a xe2x80x9cresetxe2x80x9d condition), the control processor executes an initialization sequence to place the drive in an operational state. This initialization sequence can vary from drive to drive, but generally involves initial tests of the various electronic subsystems on the PCB, after which appropriate parameters are loaded into such systems for use during operation. The spindle motor is accelerated to a velocity sufficient to aerodynamically support the heads over the discs, the heads are moved out over the disc surfaces, and the control processor reports to the host that the disc drive is fully operational and ready to receive data transfer commands.
Usually, a disc drive initialization sequence occurs after the disc drive has been at rest for an extended period of time, in which case the discs will not be spinning at the start of initialization. However, it is possible that a momentary power drop out has just occurred to cause the reset condition, or that a technician has initiated the reset condition during evaluation of the drive. In these latter two circumstances, the control processor can come out of reset and begin the initialization sequence while the discs are still spinning. It is important to determine whether the discs are spinning upon initialization, as the state of the motor will determine the appropriate manner in which drive signals are applied to accelerate the motor to the final, desired operational velocity.
Disc drives of the present generation typically use electronic commutation and back electromotive force (bemf) detection to provide spindle motor control, such as discussed in U.S. Pat. No. 5,631,999 issued to Dinsmore. Such approach generally entails applying a predetermined sequence of commutation steps to the phase windings of the spindle motor over each electrical revolution of the motor. A commutation step involves supplying the motor with current to one phase, sinking current from another phase, and holding a third phase at a high impedance in an unenergized state. Detection circuitry measures the bemf generated on the unenergized phase, compares this voltage to the voltage at a center tap, and outputs a signal at a zero crossing of the voltages; that is, when the bemf voltage changes polarity with respect to the voltage at the center tap. The point at which the zero crossing occurs is then used as a reference for the timing of the next commutation pulse, as well as a reference to indicate the position and relative velocity of the motor.
Above an intermediate velocity, such as 1000 revolutions per minute (rpm), the detection circuitry will generally be able to reliably detect rotation of the spindle motor. Hence, when the control processor comes out of reset and determines from the detection circuitry that the discs are spinning at or above this intermediate velocity, the processor directs the motor control circuitry to obtain frequency lock on the spindle motor and accelerate the motor to the final operational velocity (such as around 15,000 rpm). However, if the control processor comes out of reset and the detection circuitry does not detect the presence of zero crossing signals, the state of the motor remains unknown; the discs may be stationary, or the discs may be spinning at a low rate (less than 1000 rpm, for example).
Application of drive signals to a spindle motor while the spindle motor is in an unknown state should be avoided at all costs, since such drive signals could lead to the inadvertent rotation of the motor in the wrong direction. Rotating the spindle motor in the wrong direction, even for a very short time, can lead to premature failure of the disc drive; heads and disc surfaces can be damaged, and lubricating fluid used in hydrodynamic spindle motor bearings can be pumped out of the bearings.
To avoid such damage, control processors in prior art drives have applied a braking pulse to the motor upon initialization when no rotation of the discs is detected to ensure that the spindle motor is in a stationary, nonrotation state before the application of drive currents to the motor. Such braking pulse typically comprises the shorting together of the motor phase windings for a significant amount of time, such as 1.5 seconds, to ensure in all cases that the spindle motor is fully at rest. After the conclusion of the braking pulse, the control processor directs the motor driver circuitry to initiate acceleration of the spindle motor from a known, rest state.
While advantageously preventing damage to the drive, such pulses significantly add to the total time required to bring the drive to an operational state. Note that every time the drive is turned on after sitting for hours in an off condition, the delay is still applied to the motor. Customer requirements continue to demand reductions in the overall time required to place a disc drive in an operationally ready state, and the unnecessary application of a significant braking delay to discs already at rest runs counter to this requirement.
Accordingly, there is a need for improvements in the art whereby the rotational state of a spindle motor can be efficiently and reliably determined after a disc drive control processor comes out of a reset condition without the need for global application of a significant braking delay every time the disc drive is initialized. It is to such improvements that the present invention is directed.
In accordance with preferred embodiments, a disc drive includes a spindle motor, back electromotive force (bemf) detection circuitry which detects bemf from rotation of the spindle motor above an intermediate velocity, and commutation circuitry which electrically commutates the spindle motor in relation to the detected bemf over a range of electrical rotational positions.
Upon disc drive initialization, a control circuit of the disc drive determines whether bemf is detected from the spindle motor. If so, the control circuit directs the commutation circuitry to obtain frequency lock on the motor and accelerate the motor to a final, operational velocity at which the drive operates to transfer data between the discs and a host device. On the other hand, the absence of detected bemf from the spindle motor indicates that the spindle motor is either stationary, or is rotating at a rate below the intermediate velocity; thus, the absence of detected bemf results in uncertainty with regard to the state of the spindle motor.
Accordingly, when no bemf is detected the control circuit proceeds to identify the electrical rotational position of the spindle motor. A braking pulse of relatively short duration is applied to the spindle motor, after which the electrical rotational position of the spindle motor is again identified. A change in the electrical rotational position of the spindle motor after application of the braking pulse as compared to the electrical rotational position before application of the braking pulse provides a reliable indication that the spindle motor is still rotating, whereas no apparent change in electrical rotational position indicates that the spindle motor is at rest.
When the spindle motor is determined to be at rest, the spindle motor is accelerated from rest to the final, operational velocity. Alternatively, when the spindle motor is determined to be still rotating, another braking pulse is applied and electrical rotational position of the spindle motor is again identified. The process continues until no apparent change is detected in motor position, after which the motor is accelerated to the operational velocity.
The electrical rotational position of the spindle motor is preferably determined by sequentially applying a drive pulse to each of a plurality of commutation states respectively corresponding to each of the electrical rotational positions. A corresponding rise time for a resulting voltage induced by application of each said drive pulse is measured. The rise time is established by the impedance of the spindle motor, and the impedance of the spindle motor is established by the electrical rotational position of the motor. The relative values of the various rise times will thus readily lead to correct identification of the existing electrical rotational position of the motor.
An advantage of this approach is that uncertainty in the rotation of a spindle motor upon initialization can be quickly and reliably resolved without the need to apply a braking pulse of substantial duration to the spindle motor each time that the disc drive is initialized.
These and various other features and advantages which characterize the claimed invention will be apparent from a reading of the following detailed description and a review of the associated drawings.